21699657 has 24 divisors (see below), whose sum is σ = 37151296. Its totient is φ = 12398832.

The previous prime is 21699647. The next prime is 21699661. The reversal of 21699657 is 75699612.

It is a happy number.

It is not a de Polignac number, because 21699657 - 2⁷ = 21699529 is a prime.

It is a super-2 number, since 2×21699657² = 941750227835298, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21699607) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4678 + ... + 8079.

Almost surely, 2^21699657 is an apocalyptic number.

21699657 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21699657 is a deficient number, since it is larger than the sum of its proper divisors (15451639).

21699657 is an equidigital number, since it uses as much as digits as its factorization.

21699657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12779 (or 12767 counting only the distinct ones).

The product of its digits is 204120, while the sum is 45.

The square root of 21699657 is about 4658.2890635941. The cubic root of 21699657 is about 278.9229756159.

Subtracting from 21699657 its sum of digits (45), we obtain a palindrome (21699612).

The spelling of 21699657 in words is "twenty-one million, six hundred ninety-nine thousand, six hundred fifty-seven".